Dishwasher pump and filtration system

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the art of dishwashers and, more particularly, to a pump and filtration system employed in a dishwasher.

2. Discussion of the Prior Art

In a typical dishwasher, washing fluid is pumped from a sump into upper and lower wash arms such that kitchenware retained on vertically spaced racks within a tub of the dishwasher will be sprayed with the lo washing fluid for cleaning purposes. The washing fluid is heated, filtered and recirculated. Prior to recirculating the washing fluid, the fluid is directed through one or more filters to remove soil from the fluid, with the soil being collected in a chamber. Periodically, the system will be purged in order to drain the collection chamber of the soil.

In recent years, it has become increasingly common to provide a series of straining or filtering units in connection with an overall dishwasher pumping system such that different sized soil particles are collected at varying locations. For example, a strainer can be employed to retain large soil particles, while a fine filter can be utilized to remove smaller particles. That is, the smaller particles are able to pass through the strainer, which essentially constitutes a first filtering unit, and are caught by the second or fine filter. In connection with the pumping and filtering operation, it is also known to incorporate a mincer or chopper in order to minimize soil particle size, such as just prior to a drainage operation.

Obviously, the ability of the dishwasher to thoroughly clean the kitchenware will depend on a number of factors, including the actual configuration and flow of fluid through the filtering system, as well as the manner in which pumping and draining operations are performed. Although various dishwasher pump and filtrtion systems are known in the art, there still exists a need for improvements in this field in order to further enhance the overall cleaning functions performed by dishwashers.

SUMMARY OF THE INVENTION

The present invention is directed to a pump and filtration system in a dishwasher. In accordance with a preferred embodiment of the invention, an overall dishwasher pump system includes two separate pumps, one for providing a recirculation flow of washing fluid and the other being utilized during draining or purging operations. Most preferably, all of the washing fluid to be recirculated flows past a radial strainer, through a generally U-shaped inlet trap and then to an impeller of the recirculation pump through a chopper blade and apertured plate arrangement. In this manner, any large particles are prevented from passing through the strainer, while the remainder of the fluid entrained particles are forced through the chopper blade and plate arrangement prior to reaching the impeller of the recirculation pump.

The impeller directs the recirculating fluid radially outwardly, then the fluid is forced to flow through an involute manifold. At the manifold, the recirculating fluid is directed radially inwardly and then up to respective upper and lower wash arms. A flow conduit leading to the upper wash arm is provided with a sampling port which directs a percentage of the fluid flow into a filter chamber. The upper wall or top of the filter chamber is generally defined by one or more fine mesh filter screens that open into the dishwasher tub basin. At one annular position about the filter chamber is provided a collection chamber that leads to a flapper valve and then to a drain port. The drain port is connected to an inlet of the drain pump. With this arrangement, a percentage of the recirculating fluid flow is directed through the sampling port wherein any particles therein will settle in the collection chamber. Fluid in the filter chamber is permitted to flow upwardly through the fine mesh filter screen(s). Periodically, at timed intervals, drainage operations are performed to purge the collection chamber.

In the most preferred form of the invention, an overflow tube, which is in fluid communication with the filter chamber, extends upwardly along the rear wall of the tub basin. When the fine mesh filter becomes clogged, fluid will be forced to flow up the overflow tube. A separate filter is provided within a housing atop the tube in order to prevent soiled fluid from the filter chamber reaching the tub basin through the overflow tube. In this manner, the recirculated fluid can continue to be filtered, even while the fine mesh filter is clogged, until a timed drainage operation is performed.

In further accordance with the most preferred embodiment of the present invention, a filter guard is secured to the housing of the recirculation pump, with the filter guard extending over portions of the fine mesh filter. More specifically, the filter guard is mounted directly above the fine filter and has an outer wall which is angled to protect or shield the fine filter from damage, such as from utensils or the like falling thereon within the tub basin, as well as visually obscuring the fine filter. The filter guard preferably has a curved underside for directing downward sprays from the lower wash arm onto the fine filter in order to backwash the fine filter for cleaning purposes. In addition, the filter guard includes wash out areas for flushing out any trapped food particles.

Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is an upper right perspective view of a dishwasher constructed in accordance with the present invention, with a door of the dishwasher being open;

<figref idref="DRAWINGS">FIG. 2</figref> is another perspective view of the dishwasher of <figref idref="DRAWINGS">FIG. 1</figref> with the door open;

<figref idref="DRAWINGS">FIG. 3</figref> is a perspective view of an overall pump and filtration system incorporated in the dishwasher of the invention;

<figref idref="DRAWINGS">FIG. 4</figref> is an isometric, cross-sectional view through both a tub basin and the overall pump and filtration system of the dishwasher of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 5</figref> is a perspective, cross-sectional view through the tub basin and the pump/filtration system;

<figref idref="DRAWINGS">FIG. 6</figref> is an elevational, cross-sectional view through the tub basin and the pump/filtration system;

<figref idref="DRAWINGS">FIG. 7</figref> is another elevational, cross-sectional view through the tub basin and the pump/filtration system;

<figref idref="DRAWINGS">FIG. 8</figref> is a perspective view of a flapper valve incorporated in the pump and filtration system of the invention;

<figref idref="DRAWINGS">FIG. 9</figref> is an enlarged, perspective view of the recirculation pump, along with the lower wash arm, shown in the overall system of <figref idref="DRAWINGS">FIG. 3</figref>;

<figref idref="DRAWINGS">FIG. 10</figref> is an upper perspective view of a filter guard shown mounted atop the recirculation pump in <figref idref="DRAWINGS">FIG. 9</figref>;

<figref idref="DRAWINGS">FIG. 11</figref> is a lower perspective view of the filter guard of <figref idref="DRAWINGS">FIG. 9</figref>;

<figref idref="DRAWINGS">FIG. 12</figref> is a perspective view of a modified water conduit and overflow tube arrangement for the dishwasher of <figref idref="DRAWINGS">FIG. 1</figref>; and

<figref idref="DRAWINGS">FIG. 13</figref> is a block diagram of a control unit for the dishwasher.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With initial reference to <figref idref="DRAWINGS">FIGS. 1–3</figref>, a dishwasher constructed in accordance with the present invention as generally indicated at 2. As shown, dishwasher <b>2</b> includes a tub <b>5</b> which is preferably injection molded of plastic so as to include integral bottom, side, rear and top walls <b>8</b>–<b>12</b> respectively. Within the confines of walls <b>8</b>–<b>12</b>, tub <b>5</b> defines a washing chamber <b>14</b> within which soiled kitchenware is adapted to be placed upon shiftable upper and lower racks (not shown), with the kitchenware being cleaned during a washing operation in a manner widely known in the art. Tub <b>5</b> has attached thereto a frontal frame <b>16</b> which pivotally supports a door <b>20</b> used to seal chamber <b>14</b> during a washing operation. In connection with the washing operation, door <b>20</b> is preferably provided with a detergent tray assembly <b>23</b> within which a consumer can place liquid or particulate washing detergent for dispensing at predetermined portions of the washing operation. Of course, dispensing detergent in this fashion is known in the art such that this arrangement is only being described for the sake of completeness.

Disposed within tub <b>5</b> and, more specifically, mounted within a central opening <b>27</b> (see <figref idref="DRAWINGS">FIGS. 4–7</figref>) formed in bottom wall <b>8</b> of tub <b>5</b>, is a pump assembly <b>30</b>. In the preferred embodiment and as illustrated in these figures, pump assembly <b>30</b> includes a main housing <b>33</b>, an annular, radial outermost strainer <b>36</b> and a filter guard <b>39</b>. A detailed description of the exact structure and operation of pump assembly <b>30</b> will be described more fully below. Extending about a substantial portion of pump assembly <b>30</b>, at a position raised above bottom wall <b>8</b>, is a heating element <b>44</b>. In a manner known in the art, heating element <b>44</b> preferably takes the form of a sheath, electric resistance-type heating element.

In general, pump assembly <b>30</b> is adapted to direct washing fluid to at least a lower wash arm <b>47</b> and a conduit <b>51</b>. As depicted, conduit <b>51</b> includes a substantially horizontal, lower section <b>53</b> extending away from main housing <b>33</b> of pump assembly <b>30</b>, a vertical section <b>54</b> which generally extends along rear wall <b>11</b>, and a generally horizontally extending upper section <b>55</b> which rotatably supports an upper wash arm <b>59</b>. Vertical section <b>54</b> has attached thereto a wash fluid diverter <b>66</b> which defines upper and lower ports <b>68</b> and <b>69</b>. Although not considered part of the present invention, each of upper and lower ports <b>68</b> and <b>69</b> has associated therewith a valve, such as a flapper element indicated at <b>72</b>, for preventing any water flowing through conduit <b>51</b> from exiting either of port <b>68</b> or <b>69</b> unless structure is inserted into a respective port <b>68</b>, <b>69</b> so as to deflect a respective flapper element <b>72</b>. In general, wash fluid diverter <b>66</b> can actually be formed with a varying number of ports ranging from 1 to 3 or more. The overall wash fluid diverter <b>66</b> is actually designed to cooperate with a vertically adjustable upper rack (not shown) which would carry an associated underside wash arm and respective piping that would become aligned with and project into a respective port <b>68</b>, <b>69</b> in order to deflect flapper element <b>72</b> so as to provide an additional wash arm used to further spray washing fluid upon kitchenware, thereby supplementing lower wash arm <b>47</b> and upper wash arm <b>59</b> during a washing operation within dishwasher <b>2</b>. In general, vertically adjustable racks, as well as multi-port wash fluid diverters are known in the art such that this structure will not be described further here.

Pump assembly <b>30</b> has associated therewith a drain port <b>76</b> to which is attached a drain pump <b>79</b>. Drain pump <b>79</b> is secured beneath bottom wall <b>8</b> of tub <b>5</b> through the use of a suspension bracket <b>82</b>. Drain pump <b>79</b> has associated therewith a drain hose <b>85</b> including at least one corrugated or otherwise curved portion <b>89</b> that extends about an arcuate hanger <b>92</b> provided on an outside surface of side wall <b>10</b>. Drain hose <b>85</b> is also preferably secured to tub <b>5</b> through various clips, such as that indicated at <b>95</b>. In any event, in this manner, an upper loop is maintained in drain hose <b>85</b> to assure proper drainage in a manner known in the art.

Also projecting from main housing <b>33</b> of pump assembly <b>30</b> is an overflow tube <b>98</b>. More specifically, overflow tube <b>98</b> includes a first end <b>99</b> leading from main housing <b>33</b> in a manner which will be detailed more fully below, as well as a second end <b>100</b> which leads into an overflow housing <b>104</b>. In accordance with the preferred embodiment shown in these drawings, overflow tube <b>98</b> is preferably integrated into conduit <b>51</b> during manufacturing, such as through a blow molding or extrusion operation. In any event, second end <b>100</b> of overflow tube <b>98</b> leads out of the overall structure defining conduit <b>51</b> to direct fluid from within overflow tube <b>98</b> into overflow housing <b>104</b>. Overflow housing <b>104</b> incorporates a coarse filter <b>106</b>. In one preferred embodiment, filter <b>106</b> has openings in the order of 20 mils. Although a removable cover could be provided to access filter <b>106</b> for replacement/cleaning purposes, filter <b>106</b> is preferably molded into housing <b>104</b> such that the entire housing/filter unit would be replaced if necessary. However, as will be detailed further below, a backwashing arrangement for filter <b>106</b> is preferably employed for cleansing purposes. In any event, further details on the construction and operation of this overflow arrangement will be provided below in describing the overall operation of pump assembly <b>30</b>.

At this point, reference will now be made to <figref idref="DRAWINGS">FIGS. 4–7</figref> in describing further details of pump assembly <b>30</b>, as well as other components of dishwasher <b>2</b>. As best shown in <figref idref="DRAWINGS">FIG. 4</figref>, side walls <b>9</b> and <b>10</b> lead into bottom wall <b>8</b> through a pair of spaced plateau portions <b>121</b> and <b>122</b>. Rollers for a lower rack (not shown) are adapted to be supported upon plateau portions <b>121</b> and <b>122</b> for movement of the rack into and out of tub <b>5</b>. In any event, bottom wall <b>8</b> includes a lower base portion <b>126</b> which slopes inwardly towards a trough <b>129</b>. Trough <b>129</b> defines an inlet trap which is generally U-shaped in cross-section as clearly shown in each of <figref idref="DRAWINGS">FIGS. 4–7</figref>. Radially inwardly of trough <b>129</b>, bottom wall <b>8</b> includes an inner radial plateau portion <b>132</b> that leads to a downwardly extending portion <b>135</b> and finally a substantially horizontally extending innermost portion <b>137</b>. Innermost portion <b>137</b> defines central opening <b>27</b> within which pump assembly <b>30</b> extends as clearly shown in these figures.

Pump assembly <b>30</b> includes a lower housing plate <b>145</b> that includes a central recess section <b>148</b> and an outer edge <b>152</b>. Spaced slightly inwardly from outer edge <b>152</b>, lower housing plate <b>145</b> is provided with a lower rib <b>155</b>. As shown, lower rib <b>155</b> extends into a notch (not labeled) defined in a seal <b>160</b>. More specifically, seal <b>160</b> is sandwiched between downwardly extending portion <b>135</b> and lower rib <b>155</b>, while also projecting along outer edge <b>152</b>. In this manner, fluid that flows through trough <b>129</b> and along inner-radial plateau portion <b>132</b> is prevented from reaching innermost portion <b>137</b>, but rather is forced to flow above lower housing plate <b>145</b>.

Pump assembly <b>30</b> has associated therewith a motor <b>165</b>. In general, motor <b>165</b> is of the type known in the art and includes a housing <b>168</b> and an associated driveshaft <b>170</b> which is rotatably supported by housing <b>168</b> through upper and lower bearing units <b>172</b> and <b>173</b>. Since the general construction and operation of motor <b>165</b> is known in the art, it will not be detailed further herein. However, it should be noted that driveshaft <b>170</b> is secured for concurrent rotation with a lower drive sleeve <b>174</b>, which is spaced from an upper sleeve <b>175</b>. Although not shown in detail, lower drive sleeve <b>174</b> is preferably formed of two parts which securely sandwiches a chopper blade <b>178</b> therebetween. In this manner, chopper blade <b>178</b>, which extends substantially parallel to but spaced vertically above lower housing plate <b>145</b>, rotates in unison with driveshaft <b>170</b> during operation of motor <b>165</b>. Arranged above chopper blade <b>178</b> is a fixed, apertured plate <b>182</b>. As clearly shown in at least <figref idref="DRAWINGS">FIGS. 4 and 5</figref>, plate <b>182</b> actually includes a plurality of spaced holes <b>184</b> which are sized to permit only predetermined sized particles entrained within washing fluid as will be detailed more fully below.

At this point, it should be noted that apertured plate <b>182</b> is actually secured to an annular rib <b>186</b> which projects downward from an intermediate housing plate <b>189</b>. Actually, intermediate housing plate <b>189</b> has arranged radially outward of annular rib <b>186</b> a plurality of annularly spaced bosses, one of which is indicated at <b>193</b> in <figref idref="DRAWINGS">FIG. 7</figref>, for securing fixed apertured plate <b>182</b> in a desired position. Intermediate housing plate <b>189</b> also includes a series of upstanding, radially spaced ribs <b>195</b>–<b>197</b> which project in a direction opposite to annular rib <b>186</b>, as well as an additional rib <b>198</b> which extends downward from intermediate housing plate <b>189</b>. For reasons which will be discussed more fully below, rib <b>198</b> actually defines a flow plate which projects into trough <b>129</b>. Ribs <b>196</b> and <b>197</b> extend upwardly substantially parallel to one another and define, in accordance with the present invention, a filter chamber <b>202</b>. A cover <b>204</b>, which includes a plurality of enlarged openings <b>206</b>, spans across ribs <b>196</b> and <b>197</b>. As best illustrated in <figref idref="DRAWINGS">FIGS. 4 and 5</figref>, each of enlarged openings <b>206</b> has associated therewith a fine mesh screen <b>207</b>, preferably having openings in the order of 75 microns or 3 mils, for filtering purposes. Filter chamber <b>202</b> is open, at one side of pump assembly <b>30</b>, to a collection chamber <b>212</b>. This arrangement is best shown in <figref idref="DRAWINGS">FIGS. 4 and 5</figref>, with these figures also indicating the manner in which cover <b>204</b> is secured to intermediate housing plate <b>189</b> as well as bottom wall <b>8</b>.

More specifically, cover <b>204</b> is provided with various annularly spaced holes, one of which is indicated at <b>214</b> aligned with a respective upstanding sleeve <b>215</b> projecting up from intermediate housing plate <b>189</b>, as well as a respective mounting boss <b>216</b> formed integral with bottom wall <b>8</b>. Upon aligning these components in this manner, mechanical fasteners, such as that indicated at <b>217</b>, are placed through a respective hole <b>214</b> and sleeve <b>215</b> and secured within respective bosses <b>216</b>. In any event, at this point, it is merely important to note that filter chamber <b>202</b> extends about a top portion of pump assembly <b>30</b> and is in fluid communication with collection chamber <b>212</b> which, as will be discussed more fully below, is in fluid communication with drain port <b>76</b> and drain pump <b>79</b>.

With further reference to each of <figref idref="DRAWINGS">FIGS. 4–6</figref>, intermediate housing plate <b>189</b> locates a pump component indicated at <b>218</b>. Rotating with pump component <b>218</b> is another pump component or impeller <b>220</b>. As shown, impeller <b>220</b> is also spaced from upper sleeve <b>175</b>. In any event, impeller <b>220</b> is drivingly connected to driveshaft <b>170</b> so as to rotate in unison with driveshaft <b>170</b> and chopper blade <b>178</b> during operation of motor <b>165</b>. Although further details will be provided below, at this point, it should be noted that components <b>218</b> and <b>220</b> collectively define a recirculating pump incorporated in the overall pump assembly <b>30</b>.

In accordance with the most preferred embodiment of the invention, arranged above impeller <b>220</b> is a fixed involute manifold <b>226</b>. Involute manifold <b>226</b> is shown to include a first involute member <b>228</b> and a second involute member <b>232</b> which are intermeshed in a manner defining a radially spiraling chamber. Second involute member <b>232</b> is preferably formed as part of a pump housing cap <b>235</b> having an outermost radial portion <b>239</b> provided with at least one annular recess <b>242</b> into which projects rib <b>195</b> of intermediate housing plate <b>189</b>. A second annular recess <b>243</b> is defined radially outwardly of annular recess <b>242</b> as clearly shown in these figures. In any event, it is merely important to note that pump housing cap <b>235</b> is fixed to intermediate housing plate <b>189</b> with at least the positioning of rib <b>195</b> in annular recess <b>242</b> creating a seal between these members. In the most preferred form of the invention shown, pump housing cap <b>235</b> actually includes an outermost radial portion, i.e., a lower region <b>239</b> that defines annular recesses <b>242</b> and <b>243</b>, an intermediate region <b>248</b> defining second involute member <b>232</b>, and an upper region <b>250</b> provided with a central opening <b>253</b>. A shaft <b>257</b> which is secured to first involute member <b>228</b> extends through both opening <b>253</b> and a sleeve <b>260</b> formed integral with lower wash arm <b>47</b> in order to rotatably support lower wash arm <b>47</b>. As also illustrated in these figures, upper region <b>250</b> also opens into lower section <b>53</b> of conduit <b>51</b>. As best shown in <figref idref="DRAWINGS">FIG. 7</figref>, prior to vertical section <b>54</b>, conduit <b>51</b> is formed with a sampling port <b>267</b> which opens into a cylinder member <b>268</b> formed as part of cover <b>204</b>. In turn, cylinder member <b>268</b> leads into filter chamber <b>202</b>.

The manner in which fluid and entrained particles flows through pump assembly <b>30</b> during operation of dishwasher <b>2</b> will now be described. In a manner known in the art, tub <b>5</b> will be initially, partially filled with water which can be further heated by activation of heating element <b>44</b>. During a washing cycle, motor <b>165</b> is activated in order to concurrently rotate chopper blade <b>179</b> and impeller <b>220</b>. In this manner, the washing fluid with entrained particles will be drawn into trough <b>129</b> between fins <b>200</b> of strainer <b>36</b>. Given the distances between the respective fins <b>200</b> of strainer <b>36</b>, any large food pieces, utensils or the like will be caught by strainer <b>36</b> in the bottom of tub <b>5</b> instead of entering pump assembly <b>30</b> where they may cause damage. The combination of strainer fins <b>200</b> and rib or flow plate <b>198</b> establishes the flow and the size of entrained soil particles which can enter pump assembly <b>30</b>. Therefore, this washing fluid, which will initially be substantially clean but which will certainly pick-up additional soil during at least initial stages of a washing operation, will flow past strainer fins <b>200</b>, down into trough <b>129</b>, beneath flow plate <b>198</b>, up an opposing portion of trough <b>29</b> to an intake chamber <b>269</b> defined between lower housing plate <b>145</b> and intermediate housing plate <b>189</b>.

As the washing fluid is being drawn in by at least the operation of impeller <b>220</b>, the washing fluid will attempt to flow through apertured plate <b>182</b>. At this point, the rotating chopper blade <b>178</b> will function to mince any entrained particles within the washing fluid, with the particles having to be chopped sufficiently in order to enable passage through apertured plate <b>182</b>. Therefore, flowing through apertured plate <b>182</b> will be a liquid having, at most, small soil particles entrained therein. When this fluid supply is directed between pump component <b>218</b> and impeller <b>220</b>, the fluid is directed radially outwardly into a pumping chamber <b>270</b>. The fluid is then forced to reverse direction and to flow through involute manifold <b>226</b>.

Therefore, at involute manifold <b>226</b>, the fluid is directed radially inwardly and then upwardly, with a portion of the fluid flowing through to and causing rotation of lower wash arm <b>47</b> and a substantial portion of the fluid being directed into conduit <b>51</b>. The portion of fluid flowing into lower wash arm <b>47</b> will be sprayed into tub <b>5</b> through nozzles, such as that indicated at <b>271</b>, provided on lower wash arm <b>47</b> in order to direct the fluid upwardly against kitchenware supported upon a lower rack, as well as a portion of the fluid downwardly as will be discussed more fully below.

With respect to the fluid flowing through conduit <b>51</b>, a small percentage of this fluid will enter sampling port <b>267</b> so as to be directed through cylinder member <b>268</b> and into filter chamber <b>202</b>. The remaining portion of the fluid in horizontal section <b>53</b> of conduit <b>51</b> will continue to flow through vertical section <b>54</b> and upper horizontal section <b>55</b> in order to reach upper wash arm <b>59</b> which is used to provide a downward flow of washing fluid onto the kitchenware. As indicated above, a portion of the fluid flowing through conduit <b>51</b> can also be diverted through a respective port <b>68</b>, <b>69</b> through the use of wash fluid diverter <b>66</b>.

The portion of the fluid that flows into filter chamber <b>202</b> will actually be forced to flow around filter chamber <b>202</b> which is open to collection chamber <b>212</b> and drain port <b>76</b>. However, when drain pump <b>79</b> is not activated, this fluid and the entrained particles therein can only initially fill up collection chamber <b>212</b> and filter chamber <b>202</b>. Once chambers <b>202</b> and <b>212</b> are filled, the fluid will be caused to flow out of pump housing <b>33</b> and back into tub <b>5</b> through the various enlarged openings <b>206</b> provided with fine mesh screen <b>207</b>. Of course, given the presence of fine mesh screen <b>207</b>, the fluid re-entering tub <b>5</b> from filter chamber <b>202</b> will be substantially cleansed of any soil having any substantial particulate size. Any soil particles which are larger than that which can flow through screen <b>207</b> will be forced to remain within filter chamber <b>202</b> and will actually find their way into collection chamber <b>212</b> due to the current flow created by incoming fluid into filter chamber <b>202</b> through sampling port <b>267</b> and gravity. In any event, this cleansed washing fluid will be mixed with the remaining fluid in tub <b>5</b> and, in fact, re-mixed with the re-circulated fluid flowing out at least lower wash arm <b>47</b> and upper wash arm <b>59</b>.

With this arrangement, continued recirculation of washing fluid will assure that all of the soil particles are finely chopped by blade <b>78</b> as all the washing fluid entering intake chamber <b>269</b> can only pass to pumping chamber <b>270</b> through chopper blade <b>178</b> and fixed apertured plate <b>182</b>. Furthermore, by continuing to provide a flow into sampling port <b>267</b> and further finely filtering particles entrained in this fluid by means of fine mesh screen <b>207</b>, the percentage of soil in the recirculated washing fluid actually becomes quite small. Of course, soil will be accumulating within collection chamber <b>212</b>, along with a certain percentage in filter chamber <b>202</b>. Furthermore, since the fluid is attempting to exit pump assembly <b>30</b> through fine mesh screen <b>207</b>, the underside of fine mesh screen <b>207</b> itself will actually start to accumulate soil and can become clogged. For this purpose, lower wash arm <b>47</b> is provided with one or more lower nozzles, one of which is indicated at <b>273</b> in <figref idref="DRAWINGS">FIG. 6</figref>, in order to direct a spray of washing fluid onto fine mesh screen <b>207</b>. Therefore, this directed flow will tend to wash particles off of fine mesh screen <b>207</b> and back into filter chamber <b>202</b> and, eventually, to collection chamber <b>212</b>.

Regardless of this arrangement, fine mesh screen <b>207</b> can become significantly clogged so as to undesirably reduce the flow of cleansed washing fluid therethrough. Obviously, such a clogged arrangement results in an increase in pressure within filter chamber <b>202</b>. Granted, a substantial increase in pressure could cause washing fluid to flow into drain hose <b>85</b> upon exceeding a drain loop head. However, in accordance with the invention, this increased pressure forces washing fluid to flow from within filter chamber <b>202</b> into overflow tube <b>98</b>, which is in direct fluid communication with filter chamber <b>202</b> as perhaps best shown in <figref idref="DRAWINGS">FIGS. 4 and 5</figref>. Therefore, washing fluid from filter chamber <b>202</b> is forced up overflow tube <b>98</b> towards overflow housing <b>104</b>. At this time, coarse filter <b>106</b> will function to at least limit the return of soil back into tub <b>5</b> until fine mesh screen <b>207</b> is cleansed as discussed further below.

In accordance with the most preferred embodiment of the invention, complete drainage operations are performed on a preprogrammed, timed basis. However, additional drain or purging operations can also be performed. In accordance with the invention, an initial drainage sequence is established depending on the dishwashing operation set by the user. For instance, if the user selects a normal wash mode, a fill operation will be performed wherein a certain amount of water, which will vary with dishwasher models (generally in the order of 6.5–8 quarts), is introduced into tub <b>5</b>. Thereafter, a main wash cycle will be entered. In accordance with the most preferred form of the invention, the main wash cycle is set at 34 minutes. The main wash cycle is then followed by a rinse cycle lasting 25 minutes. Thereafter, a 30 minute dry cycle is entered.

In the alternative, the user can select a dirty wash cycle which would result, for example, in an 8 minute pre-wash, followed by: a 28 minute main wash cycle, a pre-rinse of 10 minutes, a main rinse of 25 minutes, and a 30 minute drying period. With these configurations, the normal and dirty wash cycles would have 2 or 4 fill periods respectively. Correspondingly, there would be 2 or 4 drain operations performed, each being approximately 2 minutes in duration. Therefore, the drainage operations are pre-programmed based on the particular washing cycle selected, i.e., provided at specific lapsed time periods during an overall dishwashing operation. However, it is possible for a user to select a normal wash mode when the amount of soil on the kitchenware justifies a dirty mode. To this end, dishwasher <b>2</b> includes a turbidity sensor <b>275</b> shown mounted beneath tub <b>5</b> while projecting into washing chamber <b>14</b>, preferably in trough <b>129</b>. Of course, the use of turbidity sensors to sense soil levels in dishwashers is widely known in the art. In accordance with the present invention, if a normal wash cycle is selected but turbidity sensor <b>275</b> indicates high soil levels, the pre-programmed dirty wash cycle operational sequence will be followed. Furthermore, turbidity sensor <b>275</b> incorporates a thermistor (not separately labeled) which is used in cycling of heater element <b>44</b>. At this point, it should be noted that the location of turbidity sensor <b>275</b> within trough <b>129</b> is considered to be an advantageous feature of the invention as turbidity sensor <b>275</b> is more sensitive to turbulences developed by existing soil. Trough <b>129</b> actually functions as an air/water separator for pump assembly <b>30</b> such that the location of turbidity sensor <b>275</b> is also considered to enhance the accuracy of soil level signals.

In any case, during full or partial drainage operations, soil will be removed from at least collection chamber <b>212</b> when a combination of soil and washing fluid will be directed, through the operation of drain pump <b>79</b>, into drain hose <b>85</b>. During this time, it is preferred to continue the operation of pump assembly <b>30</b> in order that nozzles <b>273</b> can continue to enhance the cleaning of fine mesh screen <b>207</b>. In addition, following the last drain operation in a given dishwashing cycle, a spritzing step is performed wherein a small amount of water is introduced to fill up trough <b>129</b> in order to assure that turbidity sensor <b>275</b> is covered so that a film will not develop thereon.

Washing fluid will continue to be pumped into drain hose <b>85</b> while fine mesh screen <b>207</b> is being purged of food soil, at which time the washing fluid in overflow tube <b>98</b> will drop back down to a normal level. Given the inclusion of filter <b>106</b> in overflow housing <b>104</b>, only filtered washing fluid can enter tub <b>5</b> through overflow tube <b>98</b>. In the most preferred embodiment, filter <b>106</b> actually incorporates a coarse mesh screen versus the fine mesh screen <b>207</b>. Again, it should be realized that fine mesh screen <b>207</b> can become overwhelmed with food soil, particularly during pre-washes. However, coarse filter <b>106</b> performs a similar filtering function when the washing fluid with entrained soil is forced up overflow tube <b>98</b>. When a washing or rinsing operation is being performed by dishwasher <b>2</b>, it is preferred that a certain spray percentage be directed at filter <b>106</b>, such as through the angling of a number of nozzles on upper wash arm <b>59</b> or on an intermediate, rack supported wash arm (not shown). Therefore, any soil that collects in filter <b>106</b> is washed back down overflow tube <b>98</b>. When pump <b>30</b> remains activated during a drain operation, this flow of soil to drain is advantageously enhanced. During other cycles, the washing fluid sprayed on filter <b>106</b> will eventually cause collected soil to fall back to filter chamber <b>202</b> through overflow tube <b>98</b> due to gravity. There the soil would be separated from the washing fluid by fine mesh filter <b>207</b>.

During drain operations, certainly soil retained in collection chamber <b>212</b>, along with some of washing fluid within pump assembly <b>30</b>, will be expelled. However, not all the drainage must flow through intake and pumping chambers <b>267</b> and <b>270</b> in accordance with the invention. That is, it is desirable to have some direct fluid communication between tub <b>5</b> and drain pump <b>79</b>. In accordance with the present invention, this communication is performed through the incorporation of a flapper valve <b>276</b> which is arranged in collection chamber <b>212</b> as shown in <figref idref="DRAWINGS">FIGS. 4–6</figref> and <b>8</b>. In accordance with the most preferred embodiment, flapper valve <b>276</b> includes an upper rim portion <b>277</b> and a plurality of downwardly directed flaps or legs <b>278</b>. Actually, three legs <b>278</b> are shown in the preferred embodiment, with each of legs <b>278</b> constituting a wall section of collection chamber <b>212</b>, while being arranged in trough <b>129</b>. With this arrangement, when drain pump <b>79</b> is activated, the suction created in collection chamber <b>212</b> will deflect legs <b>278</b> closer together thereby permitting washing fluid from within tub <b>5</b> to directly enter collection chamber <b>212</b> and, subsequently, drain hose <b>85</b>.

More specifically, the inclusion of flapper valve <b>276</b> provides a preferential drain for collection chamber <b>212</b> and filter chamber <b>202</b> before the sump defined by tub <b>5</b>. That is, when a drain operation is performed, the initial flow of washing fluid and soil from filter and collection chambers <b>202</b> and <b>212</b> will prevent legs <b>278</b> from deflecting inward, i.e., the flow past legs <b>278</b> tends to keep legs <b>278</b> closed against sides of collection chamber <b>212</b>. Once this soil entrained fluid is drained, legs <b>278</b> will deflect inward to allow further draining of the washing fluid from tub <b>5</b>. Therefore, when legs <b>278</b> deflect inward, slots are created to allow flow to drain port <b>76</b>. During normal washing and rinsing operations, flapper valve <b>276</b> also advantageously prevents collected soil from returning to tub <b>5</b> about legs <b>278</b> when fine mesh screen <b>207</b> becomes clogged as an increase in pressure within filter chamber <b>202</b> will actually result in an outward biasing of legs <b>278</b>. To this end, flapper valve <b>276</b> can substantially enhance the effectiveness of potential, partial purging operations which really only require draining to occur until the point when legs <b>278</b> will deflect inward.

<figref idref="DRAWINGS">FIGS. 9–11</figref> will now be referenced to describe the preferred construction and function of filter guard <b>39</b>. Although filter guard <b>39</b> is illustrated in each of <figref idref="DRAWINGS">FIGS. 1–3</figref>, this structure has been removed from <figref idref="DRAWINGS">FIGS. 4–7</figref> to clearly depict other structure associated with pump assembly <b>30</b>. In any event, as shown, filter guard <b>39</b> is mounted upon main housing <b>33</b> below lower wash arm <b>47</b>. Filter guard <b>39</b> includes an outer wall <b>279</b> which; slopes from an inner radial portion towards an outer radial portion. As depicted, filter guard <b>39</b> actually extends substantially over strainer fins <b>200</b> but, more importantly, extends entirely over fine mesh screen <b>207</b>. In essence, without the presence of filter guard <b>39</b>, utensils and other objects could inadvertently fall within tub <b>5</b> and damage fine mesh screen <b>207</b>. Therefore, filter guard <b>39</b> is provided to shield fine mesh screen <b>207</b>, while outer wall <b>279</b> is angled to accommodate run-off of any washing fluid.

As clearly shown in these figures, the outer wall <b>279</b> of filter guard <b>39</b> is provided with various wash-out regions <b>280</b>, with these wash-out regions also having associated therewith mounting holes <b>281</b> in bosses <b>282</b> for securing filter guard <b>39</b> to main housing <b>33</b>. Further, along an underside of filter guard <b>39</b> at wash-out regions <b>280</b> are a plurality of ribs <b>283</b>. In addition, between adjacent bosses <b>282</b> are provided spacer ribs <b>285</b>. Indentations or recesses <b>289</b> and <b>290</b> are provided around the periphery of filter guard <b>39</b>, with recesses <b>289</b> and <b>290</b> being essentially located at mounting locations for heating element <b>44</b> as clearly illustrated in <figref idref="DRAWINGS">FIG. 1</figref>.

In a manner commensurate with outer wall <b>279</b>, filter guard <b>39</b> has an underside <b>292</b> which curves in order to enhance the directing of wash arm spray for the backwashing of fine mesh screen <b>207</b>. That is, as previously indicated, lower wash arm <b>47</b> includes at least one set of nozzles <b>273</b> for use in directing a spray to backwash and cleanse fine mesh screen <b>207</b>. Filter guard <b>39</b> is spaced sufficiently from pump housing cap <b>235</b> and nozzles <b>273</b> are suitably angled to accommodate this spray upon fine mesh screen <b>207</b>. However, the curvature of underside <b>292</b> further enhances this backwashing function. Wash-out regions <b>280</b> are provided for flushing out trapped food particles in connection with the overall filter guard <b>39</b>.

Although described with reference to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, although overflow tube <b>98</b> is shown to be integrated into conduit <b>51</b>, it is possible to provide a separate overflow tube <b>98</b><i>a </i>(see <figref idref="DRAWINGS">FIG. 12</figref>). Tube <b>98</b><i>a </i>is shown to extend adjacent to conduit <b>51</b>, but actually could be directed to another portion within tub <b>5</b> distinct from conduit <b>51</b>. That is, where conduit <b>51</b> extends generally along a central portion of rear wall <b>11</b>, it is possible to direct overflow tube <b>98</b><i>a </i>to a corner or side of tub <b>5</b>. Such an arrangement could enhance the accessibility to filter <b>106</b> if changing thereof is warranted.

Obviously, dishwasher <b>2</b> needs to perform various operations in connection with a washing operation wherein heater <b>44</b>, drain pump <b>79</b> and pump motor <b>165</b> are controlled. <figref idref="DRAWINGS">FIG. 13</figref> schematically illustrates the control system used to regulate dishwasher <b>2</b> in the manner set forth above through a controller or CPU <b>295</b> based on operator inputs made at a control panel as generically represented at <b>296</b> and signals from turbidity sensor <b>275</b>, which also includes the thermistor as discussed above, provided in tub <b>5</b> outside of pump assembly <b>30</b>. Regardless, it should be readily apparent that the present invention provides multiple stage filtrations through the use of strainer <b>36</b>, sampling port <b>267</b> and fine mesh screen <b>207</b>. In addition, employing the filter guard advantageously protects the fine mesh filter while enhancing the backwashing thereof. To this end, it is important to note that the filter guard is fixed, as opposed to rotating with the lower wash arm, thereby reducing the weight of the rotatable wash arm assembly and simplifying the balancing. In any event, it should be understood that the invention is only intended to be limited by the scope of the following claims.